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Review
. 2007 Jan 13;334(7584):94-6.
doi: 10.1136/bmj.39057.406644.68.

What is heterogeneity and is it important?

John Fletcher  1
Affiliations
Review

What is heterogeneity and is it important?

John Fletcher. BMJ. .

Abstract

This is the first in a series of occasional articles explaining statistical and epidemiological tests used in research papers in the BMJ

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Conflict of interest statement

Competing interests: None declared.

Figures

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Forest plot adapted from Tramèr et al showing statistical heterogeneity in the odds ratios for medications to prevent cutaneous allergic reactions (P for χ2 test for heterogeneity for anti-H1 combined was 0.03)
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Forest plot adapted from Winzenberg et al showing absence of statistical heterogeneity in the odds ratios for the effect of calcium supplementation on bone mineral density. SMD=standardised mean difference
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Forest plot from Oliver et al showing rate ratios (random effects model) for the effects of strategies to prevent falls
See this image and copyright information in PMC

References

    1. Tramèr M, von Elm E, Loubeyre P, Hauser C. Pharmacological prevention of serious anaphylactic reactions due to iodinated contrast media: systematic review. BMJ 2006;333:675-8. - PMC - PubMed
    1. Winzenberg T, Shaw K, Fryer J, Jones G. Effects of calcium supplementation on bone density in healthy children: meta-analysis of randomised controlled trials. BMJ 2006;333:775-8. - PMC - PubMed
    1. Oliver D, Connelly JB, Victor CR, Shaw FE, Whitehead A, Genc Y, et al. Strategies to prevent falls and fractures in hospitals and care homes and effect of cognitive impairment: systematic review and meta-analyses. BMJ 2007. doi: 10.1136/bmj.39049.706493.55 - PMC - PubMed
    1. Higgins JPT, Green S. Summarising effects across studies. Cochrane handbook for systematic reviews of interventions 4.2.6 [updated Sep 2006]; Section 8.6. In: The Cochrane Library, Issue 4. Chichester: Wiley, 2006. www.cochrane.org/resources/handbook
    1. Higgins J, Thompson S, Deeks J, Altman D. Measuring inconsistency in meta-analyses BMJ 2003;327:557-60. - PMC - PubMed

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